Investigation of oxygen-related defect engineering in nonstoichiometric vanadium oxides for electrochromic zinc-ion batteries with superior electrochromic-electrochemical performance

Abstract

Electrochromic-energy storage systems (e-ESS), which visualize the electrochemical charge–discharge process, are experiencing a rapid increase in demand for advanced applications. Electrochromic aqueous zinc-ion batteries (e-AZiBs) systems have emerged as a promising alternative due to their environmental friendliness, enhanced stability, and high volumetric energy density. In this study, we developed a non-stoichiometric vanadium oxide cathode that optimizes both electrochemical and electrochromic performance by controlling the oxygen defect concentration. By optimizing the annealing temperature, we effectively controlled the concentration of oxygen defects, which enhanced Zn2+ diffusion kinetics within the layered structure of V2O5 and promoted more reversible energy storage reactions. In particular, Ec-VO 350 sample, with the most favorable level of oxygen defects, exhibited a specific capacity of 383 mAh/g, representing a 160 % improvement in electrochemical performance compared to pristine V2O5. Additionally, the structural modifications induced by oxygen defects significantly improved electrochemical stability, achieving 98.27 % capacity retention after 500 cycles at 2 A/g, demonstrating excellent reversibility. Meanwhile, although the defect states generated by oxygen vacancies can affect the electronic structure and negatively influence electrochromic properties such as coloration efficiency and ΔT, Ec-VO 350 sample successfully achieved a coloration efficiency of 46.8 cm2/C and a ΔT of 65 %, owing to its enhanced Zn2+ diffusion kinetics despite a reduced optical bandgap. The methodology for developing the non-stoichiometric vanadium oxide cathode presented in this study offers an innovative strategy to enhance the potential for electrochromic energy storage systems (e-ESS) in advanced applications.